ISO 9001 and documentation for a Construction Company

Answer:
I recommend you start describing how the company works as a set of processes. Then, relate those processes with ISO 9001:2015 clauses

When implementing a QMS I see it as a project with two work fronts: A and B.
A is about modeling how the organization works based on what is called the process approach. Describing an organization as a set of interacting processes.
See this generic example:

Then, for each process look for what can go wrong and should be improved, look for opportunities to take advantage, and see if ISO 9001:2015 requirements are already being met. Describe those processes in order to standardize your work.
B is about where is the organization going to. It is about strategic orientation, objectives and plans to meet them. It is about overall risks and opportunities and what to do to manage them.

“(2) How to define SOPs, KPIs and necessary documents?”

Answer:
ISO 9001:2015 clause 4.4.2a ) gives a lot of freedom to organizations about which documents to create. That will be a function of the complexity of your organization, of the experience and turnover of your employees, of the requirements of customers, and current performance challenges.

The following material will provide you information about implementing ISO 9001:2015 in a Construction company:
- ISO 9001 – Case study for ISO 9001:2015 transition in a construction company - https://info.advisera.com/9001academy/free-download/case-study-for-iso-9001-2015-transition-in-a-construction-company
- ISO 9001:2015 Documentation Toolkit - https://advisera.com/9001academy/iso-9001-documentation-toolkit/
- Free webinar – The Process Approach - What it is, why it is important, and how to do it - https://advisera.com/9001academy/webinar/iso-9001-process-approach-free-webinar-on-demand/
- free online training ISO 9001:2015 Internal Auditor Course – https://advisera.com/training/iso-9001-internal-auditor-course/